1. Field of the Invention
Embodiments of the present invention generally relate to radio receivers, and more particularly to hybrid zero-IF receivers.
2. Description of the Related Art
Wireless communication systems may transfer data from a transmitter to one or more receivers using modulated radio frequency (RF) signals. Bluetooth systems are wireless communication systems governed, in part, by the Bluetooth Special Interest Group (SIG). Bluetooth system may transfer data at 1, 2, or 3 Mb/s, depending on, in part, the modulation method used to encode data symbols.
FIG. 1 is a block diagram of a prior art Bluetooth receiver 100. The Bluetooth receiver 100 includes an antenna 110, a variable gain amplifier (VGA) 120, a mixer 125, a band-pass filter 130, an analog automatic gain controller (AGC) 140 and an analog phase detector 150. Bluetooth signals occupy the 2401 through 2481 MHz range of frequencies. Bluetooth devices use frequency hopping as a form of a multiple access scheme. Each frequency band is 1 MHz wide and is used by users for a predetermined amount of time. Bluetooth signals are received by the antenna 110, and may be amplified by the VGA 120. The mixer 125 typically mixes the amplified signal with a frequency signal to produce a baseband signal. The baseband signal is provided to the band-pass filter 130, which is typically configured to remove out of band signal content from the baseband signal. The filtered signal is coupled to the analog phase detector 150 and the analog AGC 140. The analog phase detector 150 determines the transmitted data symbols from the baseband signal. In some embodiments, the analog phase detector 150 may be replaced with multi-bit analog-to-digital converters (ADCs). Data from the multi-bit ADCs may be examined to determine the transmitted data symbols. The analog AGC 140 may adjust the gain of the VGA 120 such that the amplified signal may not distort and may have a relatively high signal-to-noise ratio.
Such traditional low-IF (intermediate frequency) Bluetooth receivers operate with an architecture that typically includes band-pass filtering requiring either complex analog circuits or heavy DSP processing. Moreover, the enhanced data rates (EDR) of Bluetooth version 2.0 and 2.1 as specified by the Bluetooth SIG use phase-shift keying (PSK) modulation schemes to support 2 Mbs and 3 Mbs of data throughput. These modulation schemes may require more complex analog filters or an analog differential phase detector, which may further complicate the design of a Bluetooth receiver. As is well-known, complex analog circuit designs are relatively difficult to execute, generally require more area and power than relatively simpler analog designs and may be prone to accept noise from nearby circuits.
Therefore, what is needed is a Bluetooth receiver design with relatively simple analog filter design requirements that can support the extended data rates of Bluetooth v2.0 and v2.1.